Electroacoustic transducer comprising a membrane with a middle area comprising stiffening grooves

ABSTRACT

A membrane ( 20 ) has a membrane axis ( 5 ) and a middle area ( 50 ), a central cup-shaped depression ( 52 ) being provided around said membrane axis ( 5 ), which depression ( 52 ) preferably has a connecting channel ( 53 ), wherein the middle area ( 50 ) comprises groups of stiffening grooves ( 54, 55, 56, 57 ) which extend parallel to radial directions and of which a first group of long stiffening grooves ( 54, 55, 56 ) extends up to the depression ( 52 ), said connecting channel ( 53 ) issuing into two of the long stiffening grooves ( 55, 56 ), thus interconnecting these two long stiffening grooves ( 55, 56 ).

The invention relates to a membrane for an electroacoustic transducer,which membrane is designed to be capable of vibration with respect to amembrane axis, which has a first membrane side and a second membraneside, and which has a middle area.

The invention further relates to an electroacoustic transducer with amembrane.

An electroacoustic transducer of the kind mentioned in the firstparagraph and a membrane of the kind mentioned in the second paragraphabove are known, for example, from the patent document WO 01/60530 A1.The known electroacoustic transducer is designed for generating andproviding sound in a certain frequency range by means of the knownmembrane in conjunction with a coil connected to the membrane and bymeans of a magnet system acting on the coil. The known membrane has amembrane axis and a substantially dome-shaped middle area around themembrane axis. The shape of the membrane in the middle area is thedetermining factor for the generation and projection of medium to highfrequencies within the audible range.

The known electroacoustic transducer comprising such a known membrane isused for known purposes in comparatively small appliances, for exampleas loudspeakers in mobile telephones. It is now a major concern toconstruct such an electroacoustic transducer as small as possible so asto contribute to a miniaturization of such a mobile telephone. Anessential constructional geometry of an electroacoustic transducer isgiven by the constructional height of the transducer, and is accordinglyinfluenced by the shape of the membrane and in particular the shape ofthe middle area thereof. The known membrane has a comparatively greatconstructional height because of its dome-shaped middle area, which isvery disadvantageous in view of the desired miniaturization ofappliances as mentioned above, in which such an electroacoustictransducer with such a membrane will be used.

The invention has for its object to eliminate the drawbacks mentionedabove and to provide an improved membrane for a transducer and animproved electroacoustic transducer with a membrane.

To achieve the above object, inventive features are provided in amembrane according to the invention such that a membrane according tothe invention can be characterized as follows:

A membrane for an electroacoustic transducer, which membrane is designedto be capable of vibration with respect to a membrane axis, and whichhas a first membrane side and a second membrane side, and which has amiddle area, wherein a central cup-shaped depression is present in theregion of the membrane axis, which depression is bounded by a cup bottomwall and which is open towards the first membrane side, and wherein themembrane has stiffening grooves in its middle area which stiffeninggrooves extend substantially parallel to radial directions, and whereinat least two of said stiffening grooves extend up to the depression.

To achieve the above object, furthermore, inventive features areprovided in an electroacoustic transducer according to the inventionsuch that an electroacoustic transducer according to the invention canbe characterized as follows:

An electroacoustic transducer having a membrane, wherein the transduceris provided with a membrane according to the invention.

The provision of the inventive features achieves in a constructionallycomparatively simple manner and with little additional expenditure inpractice that a membrane with an advantageously low middle area can berealized in the case of a membrane according to the invention for anelectroacoustic transducer according to the invention, it being evenpossible to construct the middle area fully planar. Such a membrane hasvery good acoustic properties in spite of its flatness, i.e. lowconstructional height, because the presence of the stiffening groovespositively influences the mechanical properties of the membraneaccording to the invention, i.e. in particular its rigidity. The use ofan electroacoustic transducer according to the invention with a membraneaccording to the invention in appliances with thin housings is highlyadvantageous because of the flatness of the membrane according to theinvention thus made possible and the resulting small constructionalheight of the membrane and accordingly of the electroacoustictransducer.

The stiffening grooves may be open alternately towards the firstmembrane side and towards the second membrane side in a membraneaccording to the invention. It was found to be particularly advantageousin a membrane according to the invention, however, if in addition thecharacterizing features of claim 2 are provided. This is advantageousfor a simple manufacture of the membrane.

It was further found to be highly advantageous in a membrane accordingto the invention if in addition the characterizing features of claim 3are provided. The depression with its connecting channel provides theadvantage of good properties in the generation and emission of medium tohigh frequencies within the audible range.

The additional provision of the characterizing features of claim 4 in amembrane according to the invention achieves a regular and symmetricalstructure, resulting in an evenly distributed stiffness or rigidity ofthe middle area.

All stiffening grooves may extend up to the depression in a membraneaccording to the invention. It was found to be particularly advantageousif in addition the features of claim 5 are provided in such a membrane,because in this case the depression can be of small dimensions in radialdirections, which is particularly advantageous for achieving goodproperties in the generation and emission of sound.

The additional provision of the characteristics of claim 6 in a membraneaccording to the invention leads to the advantage that no undefinedmembrane portions are present, and that thus no undefined membranemovements can interfere with the projected sound during the emission ofsound.

The stiffening grooves in a membrane according to the invention may havea slightly curved, sweeping, or undulating shape. It was found to beparticularly advantageous if in addition the characterizing features ofclaim 7 are provided. This leads to a particularly good stiffening ofthe membrane in its middle area.

Furthermore, the stiffening grooves in a membrane according to theinvention may have an arcuate cross-section and/or an arcuatelongitudinal section. The groove side walls may also have an arcuategradient. The arcuate cross-section and the arcuate longitudinal sectionand the arcuate gradient of the groove side walls may be convex orconcave. It was found to be particularly advantageous, however, if inaddition the characteristics of claim 8 are provided. This achieves aparticularly high stability of the membrane.

The additional provision of the characterizing features of claim 9 in amembrane according to the invention leads to the advantage that anoptimum construction is obtained both as regards a manufacturing processfor making the membrane and as regards the stiffness of the membrane inits middle area.

The additional provision of the characterizing features of claim 10 in amembrane according to the invention leads to the advantage that thedepression, which together with the connecting channel makes anessential contribution to the stiffening of the membrane in its middlearea, has an optimized construction.

The advantages described above for a membrane according to the inventionare equally valid for an electroacoustic transducer according to theinvention.

The above and further aspects of the invention will become apparent fromthe embodiment described below and are clarified with reference to thisembodiment.

The invention will now be explained in more detail with reference to anembodiment shown in the drawings, to which, however, the invention isnot limited.

FIG. 1 is a cross-sectional view, partly diagrammatic, of anelectroacoustic transducer in an embodiment of the invention, comprisinga membrane according to an embodiment of the invention.

FIG. 2 is an oblique view from below of the membrane of the transducerof FIG. 1.

FIG. 3 is a bottom view of the membrane of FIG. 2.

FIG. 4 is an oblique view from below of the central portion of themiddle area of the membrane of FIGS. 2 and 3.

FIG. 1 shows an electroacoustic transducer 1, denoted the transducer 1for short below, which is constructed as a loudspeaker. The transducer 1has a housing 2 of synthetic resin, which housing 2 is often denoted thebasket. The housing 2 has a first stage 3 and a second stage 4, whichtwo corners 3 and 4 merge into one another. Holes H are provided in theregion between the first stage 3 and the second stage 4 so as to connectthe so-termed rear space volume to the acoustic free space. A hollowcylindrical housing portion 6 extending in the direction of a transduceraxis 5 is connected to the first stage 3. A planar housing portion 7 isconnected to the second stage 4, in which portion a circular cylindricalpassage 8 is provided.

The transducer 1 comprises a magnet system 9. The magnet system 9 isformed by a magnet 10 and a pole plate 11 and a pot 12, which pot 12 isoften denoted the outer cup and is formed by a planar pot bottom 13 anda hollow cylindrical pot wall 14. The entire magnet system 9 is fastenedto the second stage 4 of the housing 2 by means of the pot wall 14 ofthe pot 12 in that an adhesive connection (not shown) is provided in thepassage 8 between the pot wall 14 and the second stage 4. The pot 12 ofthe magnet system 9 projects with its pot bottom 13 through the passage8 in the planar housing portion 7, while a mechanically and acousticallyclosed connection is formed by the adhesive connection between theplanar housing portion 7 and the pot 12. It should be noted that theacoustically closed connection may equally well be realized by means ofa press fit.

An air gap 16 is formed between the circumferential limiting surface ofthe pole plate 11 and the end region 15 of the hollow cylindrical cupwall 14 facing the pole plate 11. A vibration coil 17 of the transducer1 is partly accommodated in the air gap 16. The vibration coil 17 can beset into vibration by means of the magnet system 9 substantiallyparallel to a vibration direction indicated in FIG. 1 by a double arrow18 and parallel to the transducer axis 5. The vibration coil 17 isconnected to a membrane 20 of the transducer 1, the construction ofwhich will be described in detail below with reference to FIGS. 2 to 4.The membrane 20 can be made to vibrate by the vibration coil 17substantially parallel to the vibration direction 18 and accordinglyparallel to the transducer axis 5. It should be noted that thetransducer axis 5 is at the same time a membrane axis 5 of the membrane20.

The membrane 20 will now be described in detail with reference to FIGS.2 to 4, from which FIGS. 2 to 4 the construction of the membrane 20 canbe gathered.

The membrane 20 comprises a first membrane side 20 a formed by its frontface and a second membrane side 20 b formed by its rear face. Themembrane 20, which is made of a polycarbonate foil in the present case,has a middle area 50 and the membrane axis 5 mentioned above. Themembrane 20 further has an annular outer region 21, by means of whichouter region 21 the membrane 20 is fastened to the housing 2 of thetransducer 1 of FIG. 1. Between the middle area 50 and the outer region21 there is an annular pleated region 22 which is of circular annularshape in this case and immediately adjoins the outer region 21.

The middle area 50 of the membrane 20 is advantageously given aparticularly low construction, which leads to an advantageously smallconstructional height of the electroacoustic transducer 1 of which themembrane 20 forms part. The middle area 50 comprises an annularconnecting region 51 with elevations, which connecting region 51 servesfor fastening to the vibration coil 17. Furthermore, the middle area 50has a central cup-shaped depression 52 in the region of the membraneaxis 5, which depression 52 is of cylindrical shape in this case and hasa circular cup bottom wall 52 a and a hollow cylindrical cup side wall52 b. The depression 52 is open towards the first membrane side 20 a.FIG. 4 shows the middle area 50 with the central cup-shaped depression52 in detail. It can be noted that the depression 52 may alternativelyhave a cuboid or some other shape, for example a prismatic shape. Thedepression 52 has a connecting channel 53, which connecting channel 53leads into the cup bottom wall 52 a and is open towards the secondmembrane side 20 b, and is bounded by two planar channel side walls 53 aand 53 b and a planar channel bottom wall 53 c.

Four long stiffening grooves 54 and two further long stiffening grooves55 and 56 are present in the middle area 50, which long stiffeninggrooves 54, 55, 56 form a first group of stiffening grooves which areopen towards the second membrane side 20 b and extend from an edge ofthe pleated region 22 up to the depression 52. The long stiffeninggrooves 54, 55, 56 are regularly arranged in a circumferential directionof the middle region 50 at mutual angles of 60° each time, so that thelong stiffening grooves 55 and 56 are diametrically opposed, and theinterposed connecting channel 53 of the depression 52 issues into thetwo long stiffening grooves 55 and 56 and accordingly interconnectsthese two long stiffening grooves 55 and 56. Furthermore, six shortstiffening grooves 57 are present, which short stiffening grooves 57form a second group of stiffening grooves. The short stiffening grooves57 are arranged in the circumferential direction at angles of 30° to thelong stiffening grooves 54, 55, 56 each time and also extend from theedge of the pleated region 52 in the direction of the depression 52, butthey terminate before reaching this depression 52 each with asemi-circular end portion. The fact that the short stiffening grooves 57do not extend fully to the depression 52 but only the stiffening grooves54, 55, 56 extend up to the depression 52 achieves that an advantageousstiffening of the middle area 50 is given and the depression 52 can beof comparatively small dimensions. This has a particularly favorableinfluence on the generation and emission of medium to high frequenciesin the audible range by the transducer 1, which is capable of generatingand projecting frequencies of up to approximately 10 kHz, without adisadvantageous decoupling of the middle area 50 taking place.

As is apparent from FIGS. 2 to 4, all stiffening grooves 54, 55, 56, 57extend linearly, and all stiffening grooves 54, 55, 56, 57 have asubstantially U-shaped cross-section, so that they are each bounded bytwo planar, mutually substantially parallel groove side walls 58 and 59and a planar groove bottom wall 60. Owing to the manufacture of themembrane 20 in a deep-drawing process, the groove side walls 58 and 59enclose an angle of at most 5° with one another because of a necessaryejection draft. The connecting channel 53 has a U-shaped cross-sectionwhich is smaller than the U-shaped cross-section of the long stiffeninggrooves 55 and 56, half the latter dimension in this case. It should benoted that the cross-section of the connecting channel 53 may be smallerby a different factor, for example one third or one fourth. It mayfurther be noted that the connecting channel 53 may have the samecross-section as the long stiffening grooves 55 and 56, so that itswalls lie flush with the walls of the long stiffening grooves 55 and 56.In these embodiments, however, a somewhat lesser stiffening of themiddle area 50 or the area of the central cup-shaped depression 52should be taken into account. A construction without a connectingchannel in the depression 52 is also possible, but then a lesserstiffening in the region of the depression 52 should be accepted.

It is to be noted that all stiffening grooves may extend parallel toradial directions, in which case they are laterally displaced withrespect to the stiffening grooves 54, 55, 56, 57 disclosed above.

It is further to be noted that a different number of stiffening groovesmay be provided, for example double the number or only half the numberof stiffening grooves, which stiffening grooves may again be regularlydistributed or may be irregularly distributed in circumferentialdirection.

It is further to be noted that the depression 52 may be open towards thesecond membrane side 20 b, and all stiffening grooves 54, 55, 56, 57 maybe open towards the first membrane side 20 a.

It is further to be noted that the depression 52 may comprise twomutually crossing connecting channels 53, which connecting channels 53may have the same shape or different shapes.

It is further to be noted that the connecting channel 53 may in additionhave a stiffening groove in the channel bottom wall 54 c.

Finally, it is to be noted that a spacer 19 of a foam material isconnected to the cup bottom 13 of the transducer, which spacer bears onan appliance part for damping purposes when the transducer 1 isincorporated in an appliance (mobile telephone).

1. A membrane for an electroacoustic transducer, which membrane isdesigned to be capable of vibration with respect to a membrane axis, andwhich has a first membrane side and a second membrane side, and whichhas a middle area, wherein a central cup-shaped depression is present inthe region of the membrane axis, which depression is bounded by a cupbottom wall and is open towards the first membrane side, wherein themembrane has stiffening grooves in its middle area which stiffeninggrooves extend substantially parallel to radial directions, and whereinat least two stiffening grooves of said stiffening grooves extend up tothe depression.
 2. A membrane as claimed in claim 1, wherein allstiffening grooves are open towards the second membrane side.
 3. Amembrane as claimed in claim 1, wherein the depression has a connectingchannel, which connecting channel is open towards the second membraneside and leads into the two stiffening grooves that extend up to thedepression.
 4. A membrane as claimed in claim 1, wherein the stiffeninggrooves are angularly regularly spaced in circumferential direction. 5.A membrane as claimed in claim 1, wherein the stiffening grooves arearranged in at least two groups of stiffening grooves, such that thestiffening grooves of a first group extend up to the depression, and thestiffening grooves of a second group terminate before reaching thedepression.
 6. A membrane as claimed in claim 1, wherein the stiffeninggrooves extend with their ends facing away from the depression up to anannular intermediate portion of the membrane.
 7. A membrane as claimedin claim 1, wherein the stiffening grooves extend linearly.
 8. Amembrane as claimed in claim 1, wherein the stiffening grooves each havegroove side walls which are substantially parallel to one another.
 9. Amembrane as claimed in claim 1, wherein the stiffening grooves have asubstantially U-shaped cross-section.
 10. A membrane as claimed in claim1, wherein the connecting channel has a cross-section smaller; than thecross-section of the stiffening grooves.
 11. An electroacoustictransducer having a membrane, wherein the transducer is provided with amembrane as claimed in claim 1.